NTC Compound, Thermistor and Method for Producing the Thermistor

Abstract

An NTC compound, a thermistor and a method for producing a thermistor are disclosed. In an embodiment an NTC compound includes a ceramic material of a Mn—Ni—O system as a main constituent, wherein the Mn—Ni—O system has a general composition Ni.sub.xMn.sub.2O.sub.4-δ, wherein y corresponds to a molar fraction of Ni of a total metal content of the ceramic material of the Mn—Ni—O system, which is defined as c(Ni):(c(Ni)+c(Mn)), and wherein the following applies: 0.500<x<0.610 and 0.197<y<0.240.

Claims

1-14. (canceled)

15. An NTC compound comprising: a ceramic material of a Mn—Ni—O system as a main constituent, wherein the Mn—Ni—O system has a general composition Ni.sub.xMn.sub.2O.sub.4-δ, wherein y corresponds to a molar fraction of Ni of a total metal content of the ceramic material of the Mn—Ni—O system, which is defined as c(Ni):(c(Ni)+c(Mn)), and wherein the following applies: 0.500<x<0.610 and 0.197<y<0.240.

16. The NTC compound according to claim 15, where the following applies: 0.520≤x≤0.544 and 0.206≤y≤0.214.

17. The NTC compound according to claim 15, further comprising at least ZrO.sub.2 as a dopant, where a corresponds to a content of ZrO.sub.2 and is based on 100% by weight of Ni.sub.xMn.sub.2O.sub.4-δ, and wherein the following applies: 0.58 wt %≤a≤0.72 wt %.

18. The NTC compound according to claim 15, wherein the ceramic material has a spinel structure with the general formula AB.sub.2O.sub.4, and wherein A positions are occupied at least by Ni and B positions are occupied at least by Mn.

19. The NTC compound according to claim 15, further comprising at least one B-value modifier selected from the group consisting of CuO and Al.sub.2O.sub.3.

20. The NTC compound according to claim 15, further comprising either only CuO or only Al.sub.2O.sub.3 as a B-value modifier, wherein b corresponds to a content of Al.sub.2O.sub.3 and c corresponds to a content of CuO and, based on too wt % of Ni.sub.xMn.sub.2O.sub.4-δ, the following applies: 0 wt %≤b≤13.9 wt % and 0 wt %≤c≤8.6 wt %.

21. A thermistor comprising: a ceramic main body containing the NTC compound according to claim 15.

22. The thermistor according to claim 21, wherein a composition of the thermistor is chosen such that, when kept in air at 150° C. without any electrical load, after 2000 h, the thermistor has a maximum aging of 0.59±0.093%, based on a resistance at 25° C.

23. The thermistor according to claim 21, wherein the thermistor has a B value in a range of 3,136 K to 4,528 K.

24. The thermistor according to claim 21, wherein the ceramic main body has a specific resistance ρ.sub.25° C., and wherein ρ.sub.25° C. is in a range of 48 Ωcm to 5,1540 Ωcm.

25. The thermistor according to claim 21, further comprising a protective layer containing glass or a polymer.

26. A method for producing the thermistor according to claim 21, the method comprising: forming the ceramic main body from the NTC compound by producing granules from the NTC compound, pressing the granules and then sintering the pressed granules at a maximum temperature of 1,340° C.; applying electrode layers to the sintered ceramic main body; and baking the electrode layers into the ceramic main body.

27. A method for producing the thermistor according to claim 21, the method comprising: processing the NTC compound into a ceramic sheet; printing the ceramic sheet with inner electrodes; stacking a plurality of ceramic sheets one on top of the other; pressing the stacked ceramic sheets; punching out a ceramic component from the pressed and stacked ceramic sheets; debinding the ceramic component; sintering the ceramic component to obtain the ceramic main body; and applying outer contacts to the ceramic main body.

28. The method according to claim 27, wherein a metal is selected from the group consisting of Ag, Pd and an alloy of the two elements, and wherein the metal is used for the inner electrodes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention is described in more detail below on the basis of exemplary embodiments and associated figures.

[0034] FIG. 1 shows a schematic cross section of an exemplary embodiment of a thermistor of a multilayer type of construction;

[0035] FIG. 2 shows an image of a cut of the thermistor described in FIG. 1; and

[0036] FIG. 3 shows an enlargement of the cut shown in FIG. 2.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0037] Elements that are the same, similar or appear to be the same are provided with the same designations in the figures. The figures and the relative sizes of elements in the figures were not drawn to scale.

[0038] FIG. 1 shows a schematic cross section of an exemplary embodiment of a thermistor in a multilayer type of construction, which comprises a ceramic main body 10 that contains an NTC compound according to embodiments.

[0039] Chosen for the production of the ceramic main body 10 was an NTC compound which contains as the main constituent a ceramic material with the composition Ni.sub.0.529Mn.sub.2O.sub.4-δ. The NTC compound additively contains 0.600 wt % of ZrO.sub.2 as a dopant and 13.14 wt % of Al.sub.2O.sub.3 as a B-value modifier.

[0040] For the production of the ceramic main body 10 of the thermistor, in a first step the NTC compound was processed into a ceramic sheet. Then, the ceramic sheet was printed with an inner electrode metallization of an AgPd alloy to produce first and second inner electrodes 20 and 30 of the thermistor.

[0041] In a further step, a plurality of the ceramic sheets were stacked one on top of the other in such a way as to obtain an alternating sequence of ceramic sheets with first inner electrodes 20 and ceramic sheets with second inner electrodes 30. The stack of sheets produced was pressed and a component was punched out from the pressed stack of sheets and sintered at temperatures of up to 1340° C.

[0042] For connecting the first and second inner electrodes 20 and 30 to outer contacts 20′ and 30′, a metallization of an AgPd alloy was applied to the end faces and baked in, and for further stabilization was galvanically reinforced, allowing for making electrical contact with the component. The first inner electrodes 20 are thus connected to the outer contacts 20′ and the second inner electrodes 30 are connected to the outer contacts 30′.

[0043] For further protection, the thermistor produced was coated with a protective layer 40 of glass. After keeping for 2000 h at 150° C. in air without any electrical load, the thermistor thus obtained has a deviation of its resistance at 25° C. of only 0.59±0.093%. On account of this small deviation, the thermistor thus produced meets the requirements for improving the aging stability of thermistors.

[0044] FIG. 2 shows a cut of the thermistor of a multilayer type of construction that is described in FIG. 1. The individual constituents of the thermistor, such as the NTC compound produced according to the embodiments relating to FIG. 1, the inner electrodes and the galvanically reinforced outer contacts, can be clearly identified.

[0045] FIG. 3 shows an enlarged detail of the cut of FIG. 2. The detail shows inner electrodes (gray lines) with the sintered NTC compound in between. The microstructure of the sintered NTC compound does not have any secondary phases, as a result of which the aging stability of the thermistor is significantly improved. What is more, the sintered NTC compound has a high sintered density and an outstanding connection to the inner electrodes. This shows that the NTC compound is highly suitable for production, allowing high-performance thermistors with aging stability to be created.

[0046] The invention is not restricted to the exemplary embodiments by the description of the invention made with reference to exemplary embodiments. The invention rather comprises any novel feature and any combination of features, including in particular any combination of features in the claims, even if this feature or this combination is not itself explicitly indicated in the claims or exemplary embodiments.